JPH11239298A - Electronic camera, pixel signal correction method and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic camera capable of appropriately performing correction to white blemish increasing and decreasing in correspondence to exposure time. SOLUTION: At the time of picking up the image of an object for pixel defect detection, by comparing image data for respective pixels obtained by the image pickup with reference data as the exposure time as a parameter, a control circuit 8 determines defective pixels. Thus, in the case that the exposure time is short, the number of the defective pixels to be determined by the control circuit 8 is reduced and thus, the correction of output signals is quickly performed. On the other hand, in the case that the exposure time is long, the number of the defective pixels to be determined by the control circuit 8 is increased to a required level and image quality is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for detecting a defective pixel of a solid-state imaging device and correcting an output signal from the defective pixel in an electronic camera having the solid-state imaging device.

[0002]

2. Description of the Related Art A solid-state imaging device provided in an electronic camera converts an optical image of a subject formed on a pixel into a charge (electric signal) by using a large number of pixels arranged two-dimensionally and outputs the charge. It has the function to do. By the way, some of such pixels may not be able to output a normal signal because they have a defect (pixel defect) based on dust adhesion, crystal defect or the like. For such a pixel defect, a signal that is obtained by adding an extra signal component to an output signal that should be output in accordance with the luminance of the subject is output, and a white flaw that makes the image whitish, There is a black flaw that outputs a signal obtained by subtracting a certain signal component from an output signal that should be output in accordance with the luminance, thereby making an image blackish.

[0003] When many pixel defects occur, when an image captured using such a solid-state imaging device is reproduced, the image quality may be significantly reduced. On the other hand, since a solid-state imaging device that has recently been used has at least several hundred thousand pixels, it can be said that it is actually difficult to manufacture a solid-state imaging device having no pixel defect. Therefore, it is required to use a solid-state imaging device on the assumption that a certain amount of pixel defects always exist.

[0004] On the basis of such a premise, an electronic camera which has a correction circuit for correcting an electric signal output from a pixel having a pixel defect by post-processing to improve the image quality has already been developed. According to such an electronic camera, a pixel having a pixel defect (defective pixel) of the solid-state imaging device is detected by using a pixel defect inspection device at the time of shipment from a factory, and its position is stored as information in, for example, a ROM attached to the electronic camera. By storing the information, an output signal from the defective pixel is appropriately corrected at the time of actual imaging.

[0005]

However, it has been found that the above-mentioned white flaw is a pixel defect based on a crystal defect, and may increase depending on the use environment of the solid-state imaging device. For example, white spots tend to increase as the temperature around the solid-state imaging device increases or as the exposure time increases. In such a case, at a position different from the position of the defective pixel detected under certain conditions at the time of factory shipment,
Since a new defective pixel is generated, it is possible that sufficient correction cannot be performed. Therefore, it is conceivable that exposure is performed for a long time or at a high temperature to obtain defective pixel information, and the signal of the defective pixel is always corrected based on this information.

However, white flaws that occur when the exposure time is prolonged do not appear during short-time exposure, and it is not preferable to always perform correction processing on such white flaws because the processing time is delayed. In addition, since a pixel having such a white defect functions as a normal pixel at the time of normal imaging, correction of a normal output signal from such a pixel may rather degrade image quality.

The present invention has been made in consideration of the above-described problems of the related art, and has as its object to provide an electronic camera, a pixel signal correction method, and a recording medium that can appropriately correct white spots that increase or decrease according to exposure time. And

[0008]

To achieve the above object, an electronic camera according to the present invention stores a solid-state image sensor having a plurality of pixels and information on defective pixels of the solid-state image sensor corresponding to an exposure time. Storage means for determining a defective pixel based on information on an exposure time at the time of photographing and the defective pixel information.

Further, the electronic camera according to the present invention comprises: a solid-state image sensor having a plurality of pixels; storage means for storing information on defective pixels of the solid-state image sensor corresponding to the temperature of the solid-state image sensor; Determining means for determining a defective pixel based on the temperature information of the solid-state imaging device and the defective pixel information.

On the other hand, a pixel signal correction method according to the present invention provides a method for correcting a defective pixel at the time of imaging based on information of a defective pixel corresponding to an exposure time for a solid-state imaging device having a plurality of pixels and information of an exposure time at the time of imaging. Determining, and correcting the output signal from the determined defective pixel,
It is characterized by having.

Further, the pixel signal correction method of the present invention provides a method for correcting a pixel signal based on information on a defective pixel corresponding to an exposure time for a solid-state image sensor having a plurality of pixels and information on a temperature of the solid-state image sensor at the time of image capturing. Determining a defective pixel of
Correcting the output signal from the determined defective pixel.

Further, according to the pixel signal correction method of the present invention, a solid-state imaging device having a plurality of pixels performs imaging while changing the exposure time, thereby obtaining information on defective pixels corresponding to each exposure time. Determining a defective pixel at the time of imaging based on information of the exposure time at the time of imaging and the information of the determined defective pixel; and correcting the output signal from the determined defective pixel. It is characterized by.

[0013]

According to the electronic camera of the present invention, a solid-state imaging device having a plurality of pixels, storage means for storing information on defective pixels of the solid-state imaging device corresponding to the exposure time, and information on the exposure time at the time of photographing And determining means for determining a defective pixel based on the defective pixel information. For example, in the case where the exposure time is short, the number of defective pixels determined by the determining means can be reduced. Signal correction processing can be performed quickly. On the other hand, when the exposure time is long, the number of defective pixels determined by the determining means can be increased to a necessary extent, thereby improving the image quality.

According to the electronic camera of the present invention, a solid-state imaging device having a plurality of pixels, storage means for storing information on defective pixels of the solid-state imaging device corresponding to the temperature of the solid-state imaging device, Determining means for determining a defective pixel based on the temperature information of the solid-state image sensor and the defective pixel information; for example, when the temperature of the solid-state image sensor is low, the number of defective pixels determined by the determiner is determined. Can be reduced, so that the output signal can be corrected quickly. On the other hand, when the temperature of the solid-state imaging device is high, the number of defective pixels determined by the determining means can be increased to a necessary extent, thereby improving image quality.

According to the pixel signal correction method of the present invention, a defective pixel at the time of imaging is determined based on information of a defective pixel corresponding to an exposure time for a solid-state imaging device having a plurality of pixels and information of an exposure time at the time of imaging. Determining, and correcting the output signal from the determined defective pixel,
Therefore, for example, when the exposure time is short, the number of defective pixels can be determined to be small, whereby the output signal can be corrected quickly. On the other hand, when the exposure time is long, the number of defective pixels can be determined by increasing it to a necessary degree, thereby improving the image quality.

According to the pixel signal correction method of the present invention, the imaging time is determined based on the information of the defective pixel corresponding to the exposure time for the solid-state imaging device having a plurality of pixels and the information of the temperature of the solid-state imaging device at the time of imaging. Determining a defective pixel, and correcting the output signal from the determined defective pixel. For example, when the temperature of the solid-state imaging device is low, the number of defective pixels is determined to be small. Therefore, the output signal can be corrected quickly. On the other hand, when the temperature of the solid-state imaging device is high, the number of defective pixels can be determined to be as high as necessary, thereby improving the image quality.

According to the image signal correction method of the present invention, a step of obtaining information on defective pixels corresponding to each exposure time by performing imaging while changing the exposure time using a solid-state imaging device having a plurality of pixels; It has a step of determining a defective pixel at the time of imaging based on information of an exposure time at the time of imaging and the information of the determined defective pixel, and a step of correcting an output signal from the determined defective pixel. In the case where the number of defective pixels changes due to the length of the exposure time, the number of defective pixels whose output signal should be corrected is increased or decreased according to the exposure time, thereby ensuring a quick correction process of the output signal. Image quality can be improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a digital still camera as an electronic camera according to the first embodiment. In FIG. 1, a CCD (Charge Coupled De) as a solid-state imaging device is shown.
image) The image sensor 1 performs so-called photoelectric conversion, which converts an optical image of a subject formed on the pixel into an electric signal (generates a charge), and the drive circuit 2 generates a transfer pulse. It is a circuit that generates and supplies it to the CCD 1. The CCD 1 outputs an analog electric signal based on the transfer pulse generated by the drive circuit 2.

A CDS (correlated double sampling) circuit 3 is a circuit for reducing noise, and is driven based on a driving pulse output from the driving circuit 2. The A / D conversion circuit 4 converts an input analog signal into a digital signal and outputs the digital signal. In the A / D conversion circuit 4 according to the present embodiment, it is assumed that the higher the intensity of the light incident on the pixels on the CCD 1, the larger the value of the light is converted to a digital signal. Image data for each pixel of the CCD 1 obtained through the A / D conversion circuit 4 is temporarily
It is stored in the image memory 5.

The image data stored in the image memory 5 is subjected to various types of image processing by the CPU 6 and is finally stored in a recording unit 7 composed of a recording medium such as a memory card or a magneto-optical disk.

Here, various types of image processing include processing for correcting image data of defective pixels of the CCD 1. As described later, the CPU 6 detects a defective pixel, and stores the position information (coordinates) of the defective pixel in a memory 9 provided in the control circuit 8, and corrects the image data of the defective pixel. In the processing, such position information is read out from the memory 9 to perform correction. still,
Various data used for detecting a defective pixel are also stored in the memory 9.

The liquid crystal display device 10 displays a captured image, necessary operation information, and the like. On the front surface of the CCD 1, a lens 11 for imaging light from a subject on a pixel, an aperture 12 for adjusting the amount of incident light, and a CCD
And a temperature sensor 13 for detecting the temperature of the temperature sensor 1. The detection signal of the temperature sensor 13 is input to the control circuit 8.

Further, a distance measuring means (not shown) to the subject is provided, and the control circuit 8 drives the lens driving circuit 14 to move the lens 11 to a focus position by a signal from the distance measuring means. It has become. Further, a power switch 15 and a mode switch 16 (mode selection means) for selecting a detection mode for detecting a pixel defect are provided, and a signal based on the operation of the switch is input to the control circuit 8. Has become. On the other hand, the timer 17
Are connected to the control circuit 8. Timer 17 is a CCD
The exposure time at the time of imaging 1 is detected, and a signal corresponding to the exposure time is output to the control circuit 8. The diffuser plate 21 is used when detecting a black flaw, and is not used when detecting a white flaw.

Next, detection of a white defect as a defective pixel will be described. When the mode switch 16 is turned on in order to cope with white flaws that increase with time,
Each time the power is turned on, the detection is performed.

When the user turns on the power switch 15 with the mode switch 16 turned on,
The switch signal is input to the control circuit 8, and the control circuit 8 controls the aperture 12 (light amount adjusting means) to be fully closed,
In this state, imaging is performed for one screen while the incident light is restricted by the CCD 1 (control means). CCD by such imaging
1 is stored in the image memory 5 and output from the CPU 6.
Compares the threshold value (reference data) for white defect determination stored in advance in the memory 9 with the image data of each pixel, that is, the output signal. Note that the reference data may be obtained by averaging the peripheral data of the pixel to be detected, using captured image data.

The method of obtaining the reference data will be described below with reference to the drawings. First, consider a case where four color filters as shown in FIG. 10 are arranged for each pixel. FIG.
Is a diagram showing a state in which the color filters are two-dimensionally arranged, but only the color A is displayed for easy understanding.

In FIG. 11, for the target pixel AA,
It is assumed that reference data is calculated using data of 24 pixels of the same color (color A) in the pixel of interest in the area around nine pixels around. First, a data average value of 24 pixels is obtained. This average value is used as first reference data for this pixel. The data of the pixel of interest is compared with the first reference data to determine a difference, and the difference is set as a flaw level. If the flaw level exceeds a predetermined range, the flaw is recognized as a flaw and its position information is stored in a memory. Similar processing is performed for the other colors (B, C, and D colors). Similar processing is performed for all pixels.

The flaw level to be detected at this time may not be set to the same range for all the image data. Instead, a certain area may be divided and detected by a different reference for each area. For example, dividing the screen into a central part and a peripheral part,
The central part is less than 5%, the peripheral part is less than 10%,
The conditions for flaw detection can be changed. The percentage at this time is the ratio of the defect level to the data average value of the 24 pixels around the target pixel.

When a plurality of single-color filters are used as the color filters, all the pixels adjacent to the target pixel can be used as in the case of the black-and-white image sensor. FIG. 12 is a diagram showing this example. For example, all the portions of B can be used for the target pixel BB.
In the calculation, similarly, the data average value of the peripheral pixels may be obtained, and this may be used as the first reference data.

According to the above-described imaging, since the incident light does not reach the pixel of the CCD 1, the output signal from the pixel is less than the threshold as long as the pixel is normal.
Therefore, when the output signal is equal to or larger than the threshold, it is determined that there is a defect corresponding to a white defect. The white defect is detected by such a comparison. If a white defect is detected, the position information (two-dimensional coordinates) of the corresponding defective pixel is stored in the memory 9 (storage means) of the control circuit 8.

With this configuration, every time the power switch 15 is turned on, the detection of white flaws is automatically performed, and the latest white flaw position information is stored in the memory 9. Correction corresponding to a change in the flaw can be performed.

A white defect is a pixel defect in which a certain amount of electric charge is added and accumulated in a pixel in addition to the electric charge based on the amount of incident light, and the longer the exposure time, the more such a defect. And the amount of charge stored tends to increase. Therefore, even if a pixel does not become a defect during short-time exposure, a white defect that deteriorates image quality may occur during long-time exposure. Handling of such a pixel poses a problem in correcting the output signal of the solid-state imaging device. This problem will be described more specifically.

FIG. 2 shows the amount of charge (scratch level) accumulated in a certain pixel when exposure is performed in darkness.
It is a graph calculated | required with the exposure time. For example, if 20% or more electric charge is accumulated in such a pixel, it is assumed that the user can recognize the portion as a white defect in a reproduced image. Then, if the exposure time is less than 5 seconds in actual imaging, no correction is necessary for the output signal of such a pixel. On the other hand, if the exposure time is 5 seconds or longer in actual imaging, it is necessary to ensure the image quality of the reproduced image by correcting the output signal of such a pixel.

FIG. 3 is a graph showing the number of pixels whose output signal needs to be corrected in a certain CCD together with the exposure time. FIG. 3 shows that if the exposure time is 1 second, 50 pixels need to be corrected, but if the exposure time becomes 4 seconds, the number increases to 200 pixels.
Thus, the number of defective pixels for which the output signal needs to be corrected tends to increase with the exposure time. 2 and 3
The graph shown in FIG. 3 is an example, and may show characteristics different from those in the graphs of FIGS.

In the present invention, in order to balance image quality and processing time, white flaws that increase with exposure time or temperature are corrected in accordance with the exposure time or temperature.
For such correction, the position, exposure time, or temperature of a pixel that is affected by white flaws is obtained in advance as a parameter before capturing an image of a subject. The manner in which the position of the pixel is obtained will be described below using an example of the exposure time.

First, at the time of shipment from a factory or at the time of inspection before capturing an image of a subject, the power switch 15 of the digital still camera is turned on with the mode switch 16 turned on, whereby a switch signal is input to the control circuit 8. . The control circuit 8 drives and controls the aperture 12 (light amount adjusting means) to be fully closed, drives a shutter (not shown) in a state where the incident light is restricted, and outputs a black image to the CCD 1 while changing the exposure time. Image for the screen.

Further, the output signal of the CCD 1 which captures this dark image (image for detecting a pixel defect) is stored in the image memory 5. The CPU 6 determines a threshold value for white flaw determination stored in the memory 9 in advance (for example, 20% of the total storage amount).
%) And the output signal of each pixel are compared for each exposure time. Further, the CPU 6 detects the position (two-dimensional coordinates) of a defective pixel that outputs a signal exceeding the threshold value for each exposure time, and stores the detected position in the memory 9 (storage means) of the control circuit 8.
Table 1 shows an example of the stored data of the defective pixel. For each exposure time, the position information (1-1,1-
10 etc.) are stored. In this example, the exposure time is 1/8,
Information on defective pixels is obtained for 1, 2, and 4 seconds. When temperature is used as a parameter, the temperature may be obtained in the same manner.

[0038]

[Table 1]

If the above-described inspection is performed every time the power switch is turned on, white defects that increase due to deterioration with time can be corrected, thereby improving the image quality. In addition, since white flaws tend to increase as the temperature rises, the position (two-dimensional coordinates) of a defective pixel may be determined using the ambient temperature measured using the temperature sensor 13 during white flaw inspection as a parameter.

The position of the defective pixel detected as described above and stored in the memory 9 is read out at the time of actual imaging of the subject, and is used for the correction processing of the output signal concerning the image. Hereinafter, the embodiment will be described.

FIG. 4 is a flowchart showing a process for actually capturing an image of a subject using the electronic camera according to the present embodiment, and FIG. 5 is a subroutine for determining a pixel requiring a correction process. .

First, in step S101 of FIG.
When the user turns on the power switch 15 (power ON), the flow starts. The switch SW1 is turned on (ON) when the user half-presses a shutter button (not shown), and the switch SW2 is turned on (ON) when the user fully presses the shutter button.

In step S102, the switch SW
When the switch 1 is not turned on, the electronic camera is maintained in a standby state. However, when the switch SW1 is turned on, in the next step S103, the exposure control by the control circuit 8 is performed, and the necessary aperture value and shutter speed are determined. , The exposure time is determined.

Further, in step S104, a pixel whose output signal is to be corrected is determined. More specifically, the control circuit 8 inputs the exposure time T in step S104a of the subroutine of FIG. The exposure time T is
The control target value determined in step S103 (FIG. 4) may be used, or the actual exposure time measured by the timer 17 (FIG. 1) may be used.

After inputting the exposure time T in step S104a of FIG. 5, the control circuit 8 proceeds to step S104.
At b, it is determined whether or not the exposure time T is 1/8 second or less. If it is determined that T ≦ １ ／ seconds, step S1
At 04c, the control circuit 8 reads out the information of the pixel requiring correction from the memory 9. On the other hand, step S104b
, When it is determined that T ≦ １ ／ seconds,
The flow proceeds to step S104d.

In step S104d, the control circuit 8
Determines whether the exposure time T is 1 second or less. If it is determined that T ≦ 1 second, the control circuit 8 reads from the memory 9 the information of the pixel that needs to be corrected in step S104e. On the other hand, if it is determined in step S104d that T ≦ 1 second is not satisfied, the flow proceeds to step S104.
Proceed to f.

In step S104f, the control circuit 8
Determines whether the exposure time T is 2 seconds or less. If it is determined that T ≦ 2 seconds, the control circuit 8 reads from the memory 9 the information of the pixel that needs to be corrected in step S104g. On the other hand, if it is determined in step S104f that T is not less than 2 seconds, in the present embodiment, since the exposure time T is a maximum of 4 seconds, information of a pixel that needs correction is read from the memory 9 (step S104h). ). Thereafter, the flow returns from this subroutine.

Returning to FIG. 4, in the subsequent step S105, the control circuit 8 obtains the distance to the subject by a distance measuring circuit (not shown), and the lens driving circuit 14
Is driven to the in-focus position.

If the switch SW2 is not turned on in the subsequent step S106 (that is, the shutter button is not fully pressed), the electronic camera is kept in a standby state. The shutter is driven by the control circuit 8, and the exposure is performed for the exposure time T.

After the electric charges are accumulated in the CCD 1 by the exposure, the electric charges are transferred in step S109. The charges transferred in this manner are stored as image data for each pixel in the A / D converted image memory 5.

In step S110, the control circuit 8
Performs white flaw correction on the electric charge stored in the image memory 5 based on the information of the pixel to be corrected stored in the memory 9. The mode of this correction will be described later. After such correction, the control circuit 8 proceeds to step S111.
Then, the CPU 6 performs other signal processing, and compresses the signal in step S112. Control circuit 8
Finally, an image is recorded in the recording unit 7 in step S113, and thereafter, the flow returns to step S102.

Next, the manner of correcting white spots in step S110 will be described. First, the control circuit 8
Represents the pixel to be corrected selected based on the exposure time T,
The correction processing is performed on the charge amount corresponding to the pixel in the image data read from the memory 9 and stored in the image memory 5.

In the correction of the image data in the present embodiment, the charge amount of the pixel having the defect is newly obtained by averaging the charge amount of the pixel adjacent to the pixel having the defect. . However,
It is also possible to correct image data by adding, subtracting, multiplying, and multiplying a correction value with respect to a charge amount from a defective pixel, or by multiplying and multiplying a correction term.

First, as shown in FIG. 6, the color mosaic filters provided in the CCD 1 in advance are A, B, C, D
In the case of four color filters (for example, Ye, Cy, G, and Mg), the control circuit 8 controls the defective pixels A _{n, n}
Is calculated based on one of the following formulas. The symbols A _{n and n} described later mean the amounts of charges applied to the filter color A (that is, Ye) of the pixel in the n-th column and the n-th row.

(I) First Calculation Formula _{An, n} = ( _{An-2, n-2} + _{An-2, n} + _{An-2, n + 2} + _{An, n-2} + _{An, n + 2} + _{An + 2, n-2} + _{An + 2, n} + _{An + 2, n + 2} ) / 8 (1) (ii) Second calculation formula _{An, n} = ( _{An-2, n} + A) _{n, n−2} + A _{n, n + 2} + A _{n + 2, n} ) / 4 (2) (iii) Third calculation formula _{An, n} = (A _{n, n−2} + A _{n, n + 2} ) / 2 or ( _{An-2, n} + _{An + 2, n} ) / 2 (3)

According to the average of the above equation (1), within the 5 × 5 pixel area centered on the defective pixel, the average value of the charge amounts of the eight pixels provided with the color filters of the same color as the defective pixel is calculated as:
Since the charge amount of the defective pixel is replaced with the charge amount of the defective pixel, the change in the charge amount of such a pixel and the charge amount of an adjacent pixel become natural, whereby the image quality can be improved.

According to the average of the above equation (2), within a 5 × 5 pixel area centered on the defective pixel, a pixel provided with a color filter of the same color as the defective pixel and in the same column as the defective pixel In addition, the average value of the charge amounts of the four pixels in the same row is replaced with the charge amount of the defective pixel, and it is possible to achieve harmony between improvement in image quality and improvement in processing speed.

According to the average of the above equation (3), a pixel provided with a color filter of the same color as the defective pixel in the 5 × 5 pixel area centered on the defective pixel, and having the same column as the defective pixel Alternatively, the average value of the charge amounts of the two pixels in the same row is replaced with the charge amount of the defective pixel, so that the processing speed can be improved. Note that the correction processing is similarly performed for the filter colors B, C, and D other than A.

On the other hand, as shown in FIG. 7, the color mosaic filter is a filter of three colors A, B, and C (for example, R, G, and B), and pixels relating to the filter colors B and C are defective pixels. In such a case, the charge amount can be replaced by using the expressions (1) to (3). on the other hand,
When the pixel related to the filter color A is a defective pixel, the calculation can be performed based on any of the following formulas.

(I) First calculation formula _{An, n} = (A _{n−1, n−1} + A _{n−1, n + 1} + A _{n + 1, n−1} + A _{n + 1, n + 1} ) / 4 (4) (ii) Second calculation formula _{An, n} = ( _{An-2, n-2} + _{An-2, n} + _{An-2, n + 2} + _{An-1, n-1)} + _{An-1, n + 1} + _{An, n-2} + _{An, n + 2} + _{An + 1, n-1} + _{An + 1, n + 1} + _{An + 2, n-2} + _{An + 2, n} + A _{n + 2, n + 2} ) / 12 (5)

According to the average of the above equation (4), within the 3 × 3 pixel area centered on the defective pixel, the charge amount of the four pixels at the four corners provided with the same A color filter as the defective pixel is calculated. Since the average value is replaced by the charge amount of the defective pixel, it is possible to achieve harmony between improvement in image quality and improvement in processing speed.

On the other hand, according to the average of the above equation (5), within the 5 × 5 pixel area centered on the defective pixel, the average value of 12 pixels provided with the same A color filter as the defective pixel is calculated as The charge amount of the defective pixel is replaced, and the image quality can be improved.

Further, when a three-plate type CCD as shown in FIG. 8 is used, since a color filter of A, B, C (for example, R, G, B) is provided for each CCD, a defective pixel is provided. When correcting the charge amounts of the pixels _{An and n} , the calculation can be performed based on any of the following formulas.

(I) First Calculation Formula _{An, n} = (A _{n−1, n−1} + A _{n−1, n} + A _{n−1, n + 1} + A _{n, n−1} + A _{n, n + 1} + _{An + 1, n-1} + _{An + 1, n} + _{An + 1, n + 1} ) / 8 (6) (ii) Second calculation formula _{An, n} = ( _{An-1, n- 1} + A _{n−1, n + 1} + A _{n + 1, n−1} + A _{n + 1, n + 1} ) / 4 (7) (iii) Third formula: _{An, n} = (A _{n−1, n} + _{An, n-1} + _{An, n + 1} + _{An + 1, n} ) / 4 (8) (iv) Fourth calculation formula _{An, n} = ( _{An-1, n} + _{An + 1, n} ) / 2 (9) (v) Fifth calculation formula _{An, n} = ( _{An, n-1} + _{An, n + 1} ) / 2 (10) (vi) Sixth calculation formula _{An, n} = (A _{n−1, n−1} + A _{n + 1, n + 1} ) / 2 (11) (vii) Seventh calculation formula _{An, n} = (A _{n−1, n + 1} + A _{n +) 1, n-1} ) / 2 (12)

The calculation based on the equation (6) is to calculate the average value of the charge amounts of eight pixels adjacent to the defective pixel.
The calculation based on the expression (7) is 3 × 3 around the defective pixel.
The average value of the charge amounts of the four pixels at the four corners in the pixel area is obtained.

The calculation based on the equation (8) is to calculate the average value of the electric charges of the four pixels above, below, left and right adjacent to the defective pixel. The calculation based on the equation (9) is based on the two pixels above and below the defective pixel. Is to calculate the average value of the charge amounts.

The calculation based on the expression (10) is to calculate the average value of the electric charge amounts of the two right and left pixels adjacent to the defective pixel. The calculation based on the expression (11) is the upper left and lower right adjacent to the defective pixel. The calculation based on the expression (12) is to calculate the average value of the charge amounts of the two upper right and lower left pixels adjacent to the defective pixel. Such a calculation formula may be appropriately selected from required image quality and processing speed.

As described above, according to the present embodiment,
Since the number of defective pixels to be corrected is determined in consideration of the exposure time, when the exposure time is short, the processing speed is improved by reducing the number of defective pixels to be corrected to improve the processing speed. If the time is long, the image quality can be improved by increasing the number of defects to be corrected. According to the present embodiment, even if a pixel is determined to be defective during imaging before the exposure time is long, it can be treated as a normal pixel if the exposure time is short. You can use the full performance.

FIG. 9 is a diagram showing a second embodiment of the digital still camera. According to the configuration shown in FIG.
As in the first embodiment, it is possible to detect a defective pixel and correct the charge amount corresponding to the defective pixel. In the second embodiment, the same elements as those in the configuration of FIG.

In FIG. 9, a signal processing section 41 which outputs a digital signal converted by the A / D conversion circuit 4 includes:
A signal processing circuit 42, a pixel defect detection circuit 43 as pixel defect detection means, and a pixel defect correction circuit 44 as pixel defect correction means are provided.

The signal processing circuit 42 is a circuit that performs luminance processing and color processing, and converts the luminance signal and a digital video signal as a color difference signal, for example. The pixel defect detection circuit 43 is a circuit that detects a defective pixel having a white defect in the same manner as in the first embodiment, and the position information (two-dimensional coordinates) of the defective pixel detected by the pixel defect detection circuit 43 is It is stored in the memory 9.

The pixel defect correction circuit 44 corrects the amount of charge applied to the defective pixel based on the position information (two-dimensional coordinates) of the defective pixel stored in the memory 9 and the image data based on the corrected amount of charge To the signal processing circuit 42.

Although the present invention has been described with reference to the embodiments, it should be understood that the present invention should not be construed as being limited to the above embodiments, and that modifications and improvements can be made as appropriate. is there. For example, a relational expression between the exposure time and the number of defective pixels may be obtained in advance, and the number of defective pixels at the time of imaging may be obtained by applying the actual exposure time to the relational expression. According to this aspect, for example, even when the exposure time can be changed steplessly at the request of the user, it is possible to perform an appropriate correction process on the output of the defective pixel. Note that a program that executes the pixel signal correction method according to the present embodiment includes:
It can be stored in an information medium such as an FD.

[0074]

According to the electronic camera of the present invention, a solid-state imaging device having a plurality of pixels, storage means for storing information on defective pixels of the solid-state imaging device corresponding to an exposure time, and an exposure time at the time of photographing And determining means for determining a defective pixel based on the defective pixel information and the defective pixel information, for example, when the exposure time is short, the number of defective pixels determined by the determining means can be reduced. As a result, the output signal can be corrected quickly. On the other hand, when the exposure time is long, the number of defective pixels determined by the determining means can be increased to a necessary extent, thereby improving the image quality.

According to the electronic camera of the present invention, a solid-state image sensor having a plurality of pixels, storage means for storing information on defective pixels of the solid-state image sensor corresponding to the temperature of the solid-state image sensor, Determining means for determining a defective pixel based on the temperature information of the solid-state image sensor and the defective pixel information; for example, when the temperature of the solid-state image sensor is low, the number of defective pixels determined by the determiner is determined. Can be reduced, so that the output signal can be corrected quickly. On the other hand, when the temperature of the solid-state imaging device is high, the number of defective pixels determined by the determining means can be increased to a necessary extent, thereby improving image quality.

According to the pixel signal correction method of the present invention, a defective pixel at the time of imaging is determined based on information of a defective pixel corresponding to an exposure time for a solid-state imaging device having a plurality of pixels and information of an exposure time at the time of imaging. Determining, and correcting the output signal from the determined defective pixel,
Therefore, for example, when the exposure time is short, the number of defective pixels can be determined to be small, whereby the output signal can be corrected quickly. On the other hand, when the exposure time is long, the number of defective pixels can be determined by increasing it to a necessary degree, thereby improving the image quality.

According to the pixel signal correction method of the present invention, the imaging time is determined based on the information of the defective pixel corresponding to the exposure time for the solid-state imaging device having a plurality of pixels and the temperature information of the imaging device at the time of imaging. Determining a defective pixel, and correcting the output signal from the determined defective pixel. For example, when the temperature of the solid-state imaging device is low, the number of defective pixels is determined to be small. Therefore, the output signal can be corrected quickly. On the other hand, when the temperature of the solid-state imaging device is high, the number of defective pixels can be determined to be as high as necessary, thereby improving the image quality.

According to the image signal correction method of the present invention, a solid-state imaging device having a plurality of pixels performs imaging while changing the exposure time, thereby obtaining information on defective pixels corresponding to each exposure time. It has a step of determining a defective pixel at the time of imaging based on information of an exposure time at the time of imaging and the information of the determined defective pixel, and a step of correcting an output signal from the determined defective pixel. In the case where the number of defective pixels changes due to the length of the exposure time, the number of defective pixels whose output signal should be corrected is increased or decreased according to the exposure time, thereby ensuring a quick correction process of the output signal. Image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a digital still camera as an electronic camera according to a first embodiment.

FIG. 2 is a graph showing the amount of charge (scratch level) accumulated in a pixel regardless of the amount of incident light, together with the exposure time.

FIG. 3 is a graph showing the number of pixels for which an output signal needs to be corrected in a certain CCD together with an exposure time.

FIG. 4 is a flowchart illustrating a process when actually capturing an image of a subject using the electronic camera according to the embodiment;

FIG. 5 is a subroutine for determining a pixel requiring a correction process.

FIG. 6 is a diagram schematically showing a color mosaic filter attached to a CCD.

FIG. 7 is a diagram schematically showing a color mosaic filter different from FIG.

FIG. 8 is a diagram schematically showing a color mosaic filter attached to a three-plate CCD.

FIG. 9 is a diagram illustrating a second embodiment of the digital still camera.

FIG. 10 is a diagram illustrating an example of a four-color filter.

11 is a diagram showing a state in which the filters of FIG. 10 are two-dimensionally arranged.

FIG. 12 is a diagram showing a state in which a monochromatic filter is arranged.

[Explanation of symbols]

 Reference Signs List 1 CCD 2 drive circuit 3 CDS circuit 4 A / D converter circuit 5 image memory 6 CPU 7 storage unit 8 control circuit 9 memory 10 liquid crystal display device 11 lens 12 aperture 13 temperature sensor 14 lens drive circuit 15 power switch 16 mode switch 17 Timer 21 Diffusion plate 41 Signal processing unit 42 Signal processing circuit 43 Pixel defect detection circuit 44 Pixel defect correction circuit

Claims (11)

[Claims] 1. A solid-state imaging device having a plurality of pixels, storage means for storing information on defective pixels of the solid-state imaging device corresponding to an exposure time, and information on an exposure time at the time of photographing and the defective pixel information. And a determining means for determining a defective pixel based on the electronic camera. 2. A solid-state imaging device having a plurality of pixels; storage means for storing information on defective pixels of the solid-state imaging device corresponding to a temperature of the solid-state imaging device; and temperature information of the solid-state imaging device at the time of photographing. And an deciding means for deciding a defective pixel based on the defective pixel information. 3. The apparatus according to claim 1, further comprising a correction unit configured to correct an output signal from the determined defective pixel.
Or the electronic camera of 2. 4. A defective pixel information detecting means for obtaining information on the defective pixel by comparing data of each pixel obtained by imaging at a plurality of exposure times with predetermined data. Item 4. The electronic camera according to item 1 or 3. 5. A defective pixel information detecting means for obtaining information on the defective pixel by comparing data of each pixel obtained by imaging with a plurality of solid-state imaging devices with predetermined data. The electronic camera according to claim 2. 6. The electronic camera according to claim 4, wherein the predetermined data is obtained from data of peripheral pixels of a pixel of interest. 7. A step of determining a defective pixel at the time of imaging based on information of a defective pixel corresponding to an exposure time for a solid-state imaging device having a plurality of pixels and information of an exposure time at the time of imaging. Correcting the output signal from the defective pixel. 8. A step of determining a defective pixel at the time of imaging based on information of a defective pixel corresponding to a temperature related to a solid-state imaging device having a plurality of pixels and information of a temperature of the solid-state imaging device at the time of imaging. Correcting the output signal from the determined defective pixel. 9. A step of obtaining information on defective pixels corresponding to each exposure time by performing imaging while changing an exposure time by using a solid-state imaging device having a plurality of pixels; A pixel signal correction method, comprising: determining a defective pixel at the time of imaging based on the obtained information of the defective pixel; and correcting an output signal from the determined defective pixel. 10. The pixel signal correction according to claim 7, wherein the correction of the output signal is determined based on an output signal from a pixel near the determined defective pixel. Method. 11. A recording medium in which a program for executing the pixel signal correction method according to claim 7 is described.